In recent years, there has been swift progress in the reduction in size and increase in density of semiconductor devices. Together with this, there is demand for a reduction in the thickness of semiconductor elements used in the devices, and a need for the thickness of a semiconductor wafer to be 100 μm or less is occurring. When grinding the thickness of a semiconductor wafer to 100 μm or less, or forming a device using a semiconductor wafer of 100 μm or less, warping occurs due to the strength of the semiconductor wafer being insufficient, because of which it is not possible to grind a single semiconductor wafer, or to form a device. Therefore, in order to prevent warping from occurring by reinforcing the strength of the semiconductor wafer, technology whereby a support substrate is bonded to the semiconductor wafer, and grinding or device formation carried out, has been developed.
As technology whereby a support substrate is bonded to a semiconductor wafer, there is, for example, technology whereby a semiconductor wafer is attached to a support substrate using an organic adhesive such as a polyimide or epoxy resin, or wax with a low melting point (PTL 1, 2). This technology is such that a semiconductor wafer is fixed to a support substrate using an organic adhesive or a wax with a low melting point, and thinning carried out by grinding or device formation. After the grinding or device formation, the organic adhesive is degraded by light irradiation, or the wax melted by applying heat, and the semiconductor wafer is detached from the support substrate.
Other than the organic adhesive or the wax with a low melting point, technology whereby a semiconductor wafer is fixed to a support substrate using a protective tape is also proposed as technology whereby a support substrate is bonded to a semiconductor wafer (PTL 3).
As one example of existing technology, the following is a process flow of a semiconductor device manufacturing method including a step of joining a support substrate to a semiconductor wafer using an organic adhesive. The flow of the process is preparation of a semiconductor wafer, forming a semiconductor wafer front side structure, joining a support substrate to the front side of the semiconductor wafer, thinning the semiconductor wafer, forming aback side structure, detaching the support substrate, and dicing. As the semiconductor wafer, a wafer with a thickness of 600 μm to 700 μm is common. An ion implantation into the front side, a diffusion of long duration at approximately 1,000° C., and a formation of a gate structure and front side electrode are carried out as the formation of the front side structure. The joining of the support substrate is carried out by bonding a support substrate of the same form as the semiconductor wafer using an organic adhesive. The thinning of the semiconductor wafer is carried out by grinding and etching the back side of the semiconductor wafer after joining the support substrate. The semiconductor wafer after thinning has a thickness of approximately 100 μm. An ion implantation into the back side, impurity activation by thermal processing, and formation of a back side electrode are carried out as the formation of the back side structure. The detachment of the support substrate is carried out by heating the organic adhesive joining the semiconductor wafer and support substrate, or degrading by irradiating the organic adhesive with ultraviolet light. The dicing is a step of cutting out integrated circuits, or the like, formed on the semiconductor wafer in accordance with the steps to date by cutting the semiconductor wafer with a dicing saw, thereby forming chips.
Also, technology whereby a semiconductor wafer is fixed to a support substrate using a heat resistant adhesive is also proposed as technology whereby a support substrate is bonded to a semiconductor wafer (PTL 4).